Load lifting mechanism

ABSTRACT

A lifting mechanism employing vertical screws and carrier nut members which move on the screws is disclosed. The lift mechanism is characterized by means for readily checking the degree of wear of the threads of the carrier members, the checking being facilitated by the provision of safety nuts which are linked to the carrier nuts and which will assume the load bearing function upon failure of the carrier nuts.

United States Patent 1 51 3,687,234 Gendreau 1 Aug. 29, 1972 [54] LOAD LIFTING MECHANISM [56] References Cited [72] Inventor: Jacques C. Gendreau, Myennes-sur- U ITE STATES PATENTS Loire, France 2,593,635 4/1952 Walker ..l87/8.41 [73] Ass1gnee: Fogautolube S.A., Sur-Loire, Franc 3,309,060 3/1967 Villars ..74/424.8 A 1 3,179,963 4/1965 Sturm ..254/103 [22] 1970 3,468,401 9/1969 Letz ..187/25 [21] Appl. No.: 90,758

Primary Examiner-Harvey C. Hornsby 30 Foreign Application Priority Data Ammey Dec. 8, 1969 France ..6942313 ABSTRACT A lifting mechanism employing vertical screws and U-S- Cl. carrier nut members move on the crews is dis- 254/103 closed. The lift mechanism is characterized by means [51] Int. Cl. ..B66b 11/04 for readily checking the degree of wear of the threads [58] Field of Search ..187/24, 25, 8.41, 8.54; of the carrier members, the checking being facilitated 254/103; 74/424.8 by the provision of safety nuts which are linked to the carrier nuts and which .will assume the load bearing function upon failure of the carrier nuts.

5 Claims, 3 Drawing Figures L: 1 2 \fi PATENTED Aus 29 1972 LOAD LIFIING MECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the raising and lowering of loads. More specifically, this invention is directed to lifts of the type comprising at least two rotating vertical screws. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.

2. Description of the Prior Art While not limited thereto in its utility, the present invention is particularly well suited for utilization in apparatus employed for raising and lowering motor vehicles for the purpose of servicing. In the prior art there is a type of motor vehicle lift which comprises at least two vertical columns, each column housing a rotating vertical screw. These prior art screw-type lifts also include means for setting the screws in rotation about their axis and carrier nuts engaged on each screw and having a thread corresponding to that of the screw. Arms which engage or extend under the vehicle to be lifted and thus support the vehicle in the raised position are fixed to the carrier nuts by suitable means.

The above described vertical screw type lifts are widely known and are used in many garages and service stations. Among the attributes of screw type lifts is their relatives simplicity and ease of installation.

Screw type lifts, however, have a major disadvantage. This disadvantage resides in the fact that the threads of the carrier nuts for the vehicle supporting arms have to do a great deal of work and consequently become worn. In the prior art, the wear of the carrier nut threads could not be checked until the carrier nuts had been removed; a process which required disassembly of the entire lift. As will be obvious, if the degree of wear of the carrier nuts becomes too severe, resulting from the nuts being kept in use for too long a period, there is a risk that the nuts will no longer support the weight of the lifted vehicle and will slide on the vertical screws.

SUMMARY OF THE INVENTION The present invention overcomes the above briefly discussed and other disadvantages of the prior art by providing a novel and improved screw type lift mechanism. Thus, in accordance with the present invention, means are provided for preventing the load supporting arms from suddenly dropping under the weight of the load should the threads of the carrier nuts become excessively worn. Also in accordance with the present invention, means are provided which enable the condition of the carrier nuts to be checked without dismantling of the lift.

In a preferred embodiment, the lift of the present invention comprises at least to vertical pillars or columns. Each vertical column houses a rotating vertical screw, means for setting the screw in rotation about its axis and an internally threaded carrier nut which engages the threads on the screw. As is known in the prior art, each carrier nut is secured to an arm which is intended to be engaged under a vehicle or other load which is to be raised. However, in contradistinction to the prior art, the present invention also includes, in each column or lifting mechanism, an internally threaded safety nut which cooperates with the screw. Each lifting mechanism also includes a sleeve mounted on the screw and positioned between the carrier nut and safety nut, the sleeves being arranged to slide freely on the screw. The invention also comprises means for linking the safety nut to the sleeve and the sleeve to the carrier nut; the linking mechanism providing for a predetermined amount of spacing or play between the carrier nut and sleeve.

In accordance with the above described arrangement, in normal operation the safety nuts will be subjected to little or no stress. However, should the threads of the carrier nuts become worn to the degree that the nuts fail to engage the vertical screws sufficiently to provide the required support, the load will be transferred to the safety nuts which will be able to support the load as it is lowered in complete safety.

In a preferred embodiment the means for linking the safety nut to the sleeve and the sleeve to the carrier nut comprises a pair of parallel bars. These linking bars are rigidly mounted to the exterior of the sleeve and safety nut. Extensions of the bars are provided with longitudinal slots and are juxtapositioned to the exterior of the carrier nut. The bars are maintained in position relative to the carrier nut by screws which pass through the slots and engage the carrier nuts. In the course of assembly a space will be left between the top of the sleeve and the bottom of the carrier nut. A decrease in the amount of this sleeve-carrier nut spacing is an indication that the internal threads on the carrier nut have become worn and the nut should be replaced. Restated, the screws passing through the longitudinal slots in the linking bars exert sufficient force so as to normally 0p pose any axial displacement of the sleeve with respect to the carrier nut. However, this force is not sufficient to prevent the carrier nut from sliding relative to the linking bars should the threads of the carrier nuts become worn.

An additional feature of the present invention is a construction which renders it impossible to continue to use the lifting mechanism should the threads of the carrier nut become worn; this safety feature becoming operative only after the load has been removed from the mechanism. As will be obvious, should the threads of the carrier nuts become worn all the stresses of the lift will be transferred to the safety nuts and there is the inherent risk that the safety nuts themselves would become worn after a period of use. Thus, in accordance with the present invention, the safety nuts are disposed below the sleeves, which is themselves disposed below the carrier nuts, and the vertical screws on which these elements are mounted is provided with unthreaded portions of reduced diameter at their lower ends. Accordingly, when the arms intended to support the load are in their bottom position, the safety nuts will be completely disengaged from the thread of the vertical screws. If the lift is in its raised position and the worn carrier nuts slacken their grip, the carrier nuts will drop slightly and abut against the sleeves and the load will accordingly be transferred to the safety nuts. If the operator does not notice the fault he can nevertheless lower the load. When the load supporting arms are in the bottom position, the safety nuts will become disengaged from the threads of the vertical screws and, since the worn threads of the carrier nuts will no longer be capable of engaging the vertical screws sufiiciently to permit raising a load, it will no longer be possible to employ the lift mechanism.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and numerous other advantages and objectives thereof will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various figures and in which:

FIG. 1 is a side view of a vehicle lift employing the present invention;

FIG. 2 is an enlarged, partial view of one of the lift mechanisms of the apparatus of FIG. 1; and

FIG. 3 is an enlarged cross-sectional view of the mechanism of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The vehicle lift illustrated in FIG. 1 comprises two vertical columns 1 and 2 which are supported at their lower ends from a frame 3; frame 3 being affixed to or embedded in the ground. Each of columns 1 and 2 houses bearings, not shown, in which are joumaled the ends of respective vertical screws 4 (FIGS. 2 and 3). The vertical screw 4 of column 1 has, at its upper end, a pinion which meshes with a corresponding pinion of a reduction gear driven by an electric motor 6 mounted at the top of the column. The vertical screw 4 of column 2 is driven at the same speed as the screw of column 1 via a chain drive, not shown.

The vehicle lift of FIG. 1 is provided with two horizontal arms 7 which are capable of moving vertically along the columns 1 and 2, the arms 7 being shown as extending below a motor vehicle 8, in order to enable a load to be lifted for the purpose of giving axis to the various underside parts of theload which are to be checked and/or serviced.

The arrangement of the means which enables the horizontal arm 7 associated with column 1 to be vertically displaced is identical to the mechanism which drives arm 7 of column 2. Accordingly, only the arrangement provided in column 2 will be described below. With reference now to FIG. 2, the arm 7 is affixed to a member 8 which, in turn, is affixed to a carrier nut 9. Carrier nut 9 is internally threaded and engages the threads on the vertical screw 4. It will be understood that rotation of the screw 4 in the first direction will move the arm 7 upwards while rotation of the vertical screw in the opposite direction will move arm 7 vertically downwards.

In use, the stresses on the carrier nut 9 are concentrated and predominantly located on the downwardly disposed flanks of the internal thread. These stresses will, in time, result in a degree of wear of the carrier nut thread. There is, accordingly, the risk of the threads of the carrier nut 9 giving way under the weight of the load after an extended period of use.

An internally smooth sleeve 10 is mounted on vertical screw 4 below carrier nut 9. Sleeve 10 has an internal diameter which is slightly greater than the external diameter of screw 4 and thus the sleeve is able to slide freely on the screw.

A safety nut 11 is mounted on vertical screw 4 below sleeve 10. Nut 11 is internally threaded and engages screw 4.

As may best be seen from FIG. 3, each of safety nut 11, sleeve 10 and carrier nut 9 has two longitudinal grooves 12 and 13 which are oppositely disposed when the elements are in their proper installed position. Grooves 12 and 13 are intended to receive respective linking bars 14 and 15. Bar 14 has four longitudinally aligned smooth holes 16 and one slot 17. The holes 16 in bar 14 receive screws 18 which have threaded portions which engage corresponding threaded apertures in sleeve 10 and safety nut 11; the threaded apertures in the sleeve and safety nut being at the base of groove 12. Similarly, the base of the groove 13in sleeve 10 and safety nut 11 is provided with threaded apertures which are engaged by screws 19 which pass through aligned smooth holes 20 in bar 15. Through the combined locking action of the bars and screws, the sleeve 10 and safety nut 11 are permanently located relative to one another.

The base of groove 12 in carrier nut 9 is provided with two threaded holes 21. Holes 21 receive the threaded ends of screws 22; the screws 22 having an intermediate portion of enlarged diameter between the threaded end and head. Upon installation, a spring washer 25 is installed on each of screws 22, the screws are passed through the slot 17 in bar 14 and the screw is tightened until the shoulder at the junction of the threaded and enlarged intermediate portions of the screw abuts the surface of carrier nut 9 in slot 17. Similarly, the bar 15 has a slot 26 whereby screws 28 are spring washers 29 may be installed.

The lower end 30 of vertical screw 4 is unthreaded and of smaller diameter than the threaded portion of the screw. Accordingly, when the arm 7 is in its bottom position the safety nut 11 is completely disengaged from the thread of screw 4.

When it is desired to raise a load partially or totally supported on arm 7, vertical screw 4 is caused to rotate in the appropriate direction whereby carrier nut 9 moves vertically upwards. During this lifting action the sleeve 10 and the safety nut l l, which are linked to the carrier nut 9 by the bars 14 and 15, follow the movements of the carrier nut 9. The forces exerted by spring wahsers 25 and 29 are sufficient to retain the preset positioning of the carrier nut relative to the sleevesafety nut until the threads on the safety nut engage the screw. Since only the carrier nut is supporting the load, safety nut 1 1 will do no work at this time.

As will be seen from FIGS. 2 and 3, during assembly of the mechanism a space is left between the upper end of sleeve 10 and the lower end of the carrier nut 9. Should the downwardly disposed flanks of the threads of carrier nut 9 become worn, the free space left between the carrier nut and sleeve 10 will decrease thus signifying, upon merely cursory inspection, that the carrier nut 9 should be replaced.

If a faulty carrier nut 9 is not replaced and use of the lifting mechanism is continued, wear of the threads of the carrier nut will continue until the nut is unable to support the load. When the threads of the carrier nut 9 break while a load is being supported in the raised position, the lower end of carrier nut 9 will move into contact with the upper end of sleeve 10 and the load will be transferred to the safety nut 11 via sleeve 10. The kinetic energy of the load in practically free fall, upon carrier nut thread failure, is minimized due to the small distance separating the carrier nut 9 from the sleeve 10.

The forces supplied by the spring washers are insufficient to prevent this load induced movement of the carrier nut relative to the bars 14 and 15. When the load is transferred to the safety nut 11, the arm 7 may be returned to the bottom position with safety.

When the arm has been lowered to the point where the load is supported by the ground, the safety nut 11 will be disengaged from the threads of the vertical screw 4 and will be coaxial with the unthreaded portion 30 of screw 4. If the operator has not observed the thread failure and initiates lifting of arm 7, the carrier nut 9 will not move upwards since its threads no longer cooperate with the threads of screw 4. Since the safety nut 11 is now disengaged from the threads of screw 4, the screw will rotate without imparting any vertical movement to arm 7.

Considering the vehicle lift of. FIG. 1, if only one of carrier nuts 9 is damaged it will nevertheless be impossible to raise a vehicle since only one of the arms 7 will lift.

It will be appreciated that the invention enables lifts of the type described to be made safe in a very simple and highly effective manner. It is also to be observed that the present invention avoids the possibility of leaving the lift mechanism locked in the elevated position as a result of a component .failure.

While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, the present invention has been described by way of illustration and not limitation.

What is claimed is: l. A load lifting mechanism comprising: at least a first screw member; means coupled to said first screw member for causing rotation of said screw member about its axis;

carrier means having a threaded portion which normally engages a threaded portion of said first screw member whereby rotation of said screw member will cause movement of said carrier means along a plane transverse to the axis of said screw member, said carrier means also including a load supporting portion;

safety nut means, said safety nut means having a threaded portion which corresponds with the threaded portion of said first screw member;

sleeve means positioned about said first screw member between said carrier means and said safety nut means, the inner diameter of said sleeve means being greater than the maximum outer diameter of said screw member; and

means for linking said safety nut means to said carrier means, said linking means normally providing spacing between said sleeve means and said carrier means to retain a preset positioning of the carrier means relative to the safety nut means, said linking means including:

bar means oriented parallel to the axis of said screw member, said bur means being affixed to said sleeve and safety nut means, said bar means having an extension which overlies at least a portion of said carrier means, said bar means extension being characterized by a longitudinal slot;

at least a first fastener passing through said bar means longitudinal slot and engaging said carrier means, said first fastener having a threaded portion which engages said carrier means, said first fastener also having a head portion which is spaced outwardly from said bar means; and a resilient member positioned between the head of said first fastener and the surfaces of said bar means at said either side of said slot. 2. A load lifting mechanism comprising: a first vertically oriented rotatable screw member; a second vertically oriented rotatable screw member spacially displaced from said first screw member; first carrier means having a threaded portion which normally engages a threaded portion of said first screw member, said first carrier means also including a load supporting portion;

second carrier means having a threaded portion which normally engages a threaded portion of said second screw member, said second carrier means also including a load supporting portion whereby rotation of said first and second screw members will cause vertical movement of a load extending between and supported by said first and second carrier means;

first and second safety nut means, said safety nut means respectively having threaded portions which correspond with the threaded portions of said first and second screw members;

first and second sleeve means positioned about respective of said screw members between said.

carrier means and said safety nut means, the inner diameter of each of said sleeve means being greater than the maximum outer diameter of its associated screw member;

means for linking each said safety nut means to each pair carrier means, said linking means normally providing spacing between said sleeve means and said carrier means, said linking means including;

bar means oriented parallel to the axis of each of said screw members, one of said bar means being affixed to each of said safety nut means, each of said bar means having an extension which overlies at least a portion of the carrier means on its associated screw member; and

means resiliently coupling said bar means extensions to its underlying carrier means to retain a preset positioning of the carrier means relative to their associated safety nut means.

3. The-apparatus of claim 2 wherein each of said screw members comprises:

a substantially vertically oriented member having an upper threaded portion and a lower unthreaded portion, said safety nut means being coaxial with said unthreaded portion when said lifting mechanism is in its lowest position.

4. The apparatus of claim 3 wherein said screw member comprises:

a substantially vertically oriented member having an upper threaded portion and a lower unthreaded portion, said safety nut means being coaxial with said unthreaded portion when said lifting mechanism is in its lowest position.

5. The apparatus of claim 4 wherein said bar means comprises:

a pair of parallel bars, said bars being received in slots provided at opposite sides of the external portions of said safety nut, sleeve and carrier means.

mg UNITED STATES PATENT oTTTcE QER'HFICATE @F CRECHGN Patent No. 234 Dated August 29 a 1972 Inventor(s) Jacques C. Gendreau It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE CLAIMS Claim 4, line 1, change "3" to --1-- Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A load lifting mechanism comprising: at leAst a first screw member; means coupled to said first screw member for causing rotation of said screw member about its axis; carrier means having a threaded portion which normally engages a threaded portion of said first screw member whereby rotation of said screw member will cause movement of said carrier means along a plane transverse to the axis of said screw member, said carrier means also including a load supporting portion; safety nut means, said safety nut means having a threaded portion which corresponds with the threaded portion of said first screw member; sleeve means positioned about said first screw member between said carrier means and said safety nut means, the inner diameter of said sleeve means being greater than the maximum outer diameter of said screw member; and means for linking said safety nut means to said carrier means, said linking means normally providing spacing between said sleeve means and said carrier means to retain a preset positioning of the carrier means relative to the safety nut means, said linking means including: bar means oriented parallel to the axis of said screw member, said bar means being affixed to said sleeve and safety nut means, said bar means having an extension which overlies at least a portion of said carrier means, said bar means extension being characterized by a longitudinal slot; at least a first fastener passing through said bar means longitudinal slot and engaging said carrier means, said first fastener having a threaded portion which engages said carrier means, said first fastener also having a head portion which is spaced outwardly from said bar means; and a resilient member positioned between the head of said first fastener and the surfaces of said bar means at said either side of said slot.
 2. A load lifting mechanism comprising: a first vertically oriented rotatable screw member; a second vertically oriented rotatable screw member spacially displaced from said first screw member; first carrier means having a threaded portion which normally engages a threaded portion of said first screw member, said first carrier means also including a load supporting portion; second carrier means having a threaded portion which normally engages a threaded portion of said second screw member, said second carrier means also including a load supporting portion whereby rotation of said first and second screw members will cause vertical movement of a load extending between and supported by said first and second carrier means; first and second safety nut means, said safety nut means respectively having threaded portions which correspond with the threaded portions of said first and second screw members; first and second sleeve means positioned about respective of said screw members between said carrier means and said safety nut means, the inner diameter of each of said sleeve means being greater than the maximum outer diameter of its associated screw member; means for linking each said safety nut means to each pair carrier means, said linking means normally providing spacing between said sleeve means and said carrier means, said linking means including; bar means oriented parallel to the axis of each of said screw members, one of said bar means being affixed to each of said safety nut means, each of said bar means having an extension which overlies at least a portion of the carrier means on its associated screw member; and means resiliently coupling said bar means extensions to its underlying carrier means to retain a preset positioning of the carrier means relative to their associated safety nut means.
 3. The apparatus of claim 2 wherein each of said screw members comprises: a substantially vertically oriented member having an upper threaded portion and a lower unthreaded portion, said safety nut means being coaxial with said unthreaded portion when said lifting mechanism is in its lowest position.
 4. The apparatus of claim 3 wherein said screw meMber comprises: a substantially vertically oriented member having an upper threaded portion and a lower unthreaded portion, said safety nut means being coaxial with said unthreaded portion when said lifting mechanism is in its lowest position.
 5. The apparatus of claim 4 wherein said bar means comprises: a pair of parallel bars, said bars being received in slots provided at opposite sides of the external portions of said safety nut, sleeve and carrier means. 